Turbulent Drag Reduction using Superhydrophobic Surfaces

Rothstein这项研究的目标是开发和应用一种创新的被动技术，以在湍流中产生显著的减阻效果。通过处理固体表面使其超疏水，有可能极大地影响该固体表面与流动的液体的相互作用。初步实验表明，超疏水表面可用于减少流经微通道的层流阻力高达40%。这项新的研究旨在通过拟议的实验表明，这些表面也可以用来延迟向湍流的转变，并在内部和外部湍流中产生实质性的减阻。这项拟议技术的开发可能会对现有的各种技术产生深远的影响，从而带来从减少管道流动的压降到增加船舶的航程和速度的各种好处。智能优点：超疏水表面的设计是通过对微米或纳米级表面粗糙度的材料进行化学处理使其疏水性来设计的。由于这些微米和纳米级突起的疏水性，当水接触到超疏水表面时，它不会完全湿润表面。相反，它只与表面拓扑的峰部接触，从而形成无剪切的空气-水界面。PI通过直接测速以及与数值模拟和分析理论的比较表明，层流的减阻是由于固体与流动流体接触的有效表面积减小以及无剪切气水界面的存在所致。通过在流动中诱导有效滑移，减少有效表面积和降低壁面剪应力，这些超疏水表面也应该在湍流中产生相当大的减阻作用。初步实验表明，槽道湍流的减阻效果可达50%以上，但这方面的工作还很有限。由于仍有大量的设计空间有待开发，这一数字可能会大幅增加。这项技术代表了一种新的被动湍流减阻方法，它不需要对输送的流体进行任何修改，也不需要设备的主动控制，只需要开发和使用疏水的微表面和纳米表面。将测试各种图案和超疏水材料，以使用耐用、长寿命和易于应用的超疏水表面来最大限度地减少湍流阻力。这些表面将在许多不同的流动中被研究，包括槽道流动，流经平板的流动和流经许多不同的钝化和流线型物体的流动。在这个建议中，我们将i)探索一些不同的超疏水表面设计，以试图更好地理解起源和缩放或湍流减阻，ii)将湍流减阻测量扩展到高雷诺数，以研究超疏水减阻现象是过渡效应还是在较高速度下是稳健的，Iii)调查空气-水界面形状和偏转的重要性，以及iv)调查超疏水表面对流经钝体或流线型物体的流动的影响，这些物体存在滞流点并有望分离。广泛的影响：拟议的研究计划将基本的实验润湿现象和流体动力学与商业和工业应用联系起来，在商业和工业应用中，减阻可以节省大量资金，减少国家对化石燃料的依赖，并显著减少商业和军用航运的二氧化碳足迹。这一研究项目的结果应该会带来一种关于湍流减阻的全新思维方式。该项目有几个教育部分，包括本科生参与研究，K-12外联，以及通过设在马萨诸塞州大学的NEAGEP中心从代表性不足的群体中招募学生。

0967531RothsteinThe research has the objective to develop and apply an innovative new passive technique for producing significant drag reduction in the turbulent flows. By treating a solid surface to make it superhydrophobic it is possible to dramatically affect how this solid surface interacts with a flowing liquid. Preliminary experiments have shown that superhydrophobic surfaces can be utilized to reduce drag in laminar flows through microchannels by up to 40%. The new research is aimed to show through the proposed experiments that these surfaces can also be used to delay the transition to turbulence and produce substantial drag reduction in both internal and external turbulent flows. The development of the proposed technology could have a profound effect on a huge variety of existing technologies, resulting in benefits ranging from a reduction in the pressure drop in pipe flows to an increase in range and speed of ships.Intellectual Merit:Superhydrophobic surfaces are engineered by taking materials with micron or nanoscale surfaces roughness and chemically treating them to make them hydrophobic. Because of the hydrophobicity of these microscale and nanoscale protrusions, when water is brought in contact with a superhydrophobic surface, it does not fully wet the surface. Instead, it remains in contact with only the peaks of the surface topology resulting in a shear free air water interface. The PI has shown through direct velocity measurements and comparison to numerical simulations and analytical theory that drag reduction in laminar flows results from the reduction in the effective surface area of the solid in contact with the flowing fluid and the presence of this shearfree air water interface. By inducing an effective slip, reducing the effective surface area and reducing the wall shear stress in a flow, these super-hydrophobic surfaces should also produce considerable drag reduction in turbulent flows. The preliminary experiments show upwards of 50% drag reduction in turbulent channel flows, however the work was narrowly focused and limited. With a wealth of design space still to be explored this number could increase substantially. This technique represents a new passive approach to turbulent drag reduction that does not require any modification of the transported fluid or active control by the device only the development and use of hydrophobic micro and nanopatterned surfaces. Various patterns and superhydrophobic materials will be tested to maximize turbulent drag reduction using durable, long-lived and easily applied superhydrophobic surfaces. These surfaces will be investigated in a number of different flows including channel flow, flow past a flat plate and flow past a number of different blunt and streamlined objects.In this proposal we will i) explore a number of different designs of superhydrophobic surfaces to attempt to better understand the origins and scaling or turbulent drag reduction, ii) extend the turbulent drag reduction measurements to high Reynolds numbers to investigate if the superhydrophobic drag reduction phenomena is a transition effect or robust at higher speeds, iii) investigate the importance of air-water interface shape and deflection and iv) investigate the impact of superhydrophobic surfaces on the flow past blunt or streamlined bodies where stagnation points are present and separation is expected.Broader Impacts: The proposed research program bridges fundamental experimental wetting phenomena and fluid dynamics with commercial and industrial applications where drag reduction could save significant amount of money, reduce the countrys dependence on fossil fuels and dramatically reduce the CO2 footprint of commercial and military shipping. The results from this research program should lead to a whole new way of thinking about turbulent drag reduction. The project has several educational components including involvement of undergraduates in the research, K-12 outreach and the recruitment of students from underrepresented groups through the NEAGEP centered at UMASS.